March 14, 2011 -- Many men with prostate cancer will get treatments to block male hormones like testosterone in an effort to keep their cancer from spreading.

There are several recognized side effects associated with those therapies, including hot flashes, loss of interest in sex, erectile dysfunction, bone loss, mood changes, and weight and body composition shifts. Body composition is a loss of muscle and bone mass with an increase in fat mass.

Now a new study shows that the weight gain -- about 9 pounds, on average -- associated with a form of hormone therapy called androgen deprivation therapy (ADT) appears to level off after the first year of treatment. It’s a finding that experts say is useful in helping doctors and patients who are trying to manage that extra girth, which studies have shown may increase the risks of diabetes and heart disease.

“The changes in body composition are a substantial side effect for which we don’t have a great solution yet,” says Philip J. Saylor, MD, instructor in medicine and a clinical oncologist at Massachusetts General Hospital, in Boston. “It’s helpful to know that it doesn’t lead to progressive changes throughout the course of a prolonged treatment. It’s helpful to know that most of the change happens early and that additional therapy doesn’t bring additional changes in body composition.” Saylor reviewed the study for WebMD but was not involved in the research.

The study’s researchers say the finding underscores the need for doctors to use these treatments, which include either surgical removal of the testes or drug therapy, conservatively.

“I’m using hormonal therapy a lot less than I was a few years ago because I do realize it is a very effective, albeit toxic therapy,” says study researcher Stephen J. Freedland, MD, associate professor at the Duke Prostate Center and a staff physician Veterans Affairs Medical Center, in Durham, N.C.

“There’s a growing body of data, to which our study contributes, that says there are clearly side effects with these therapies, so let’s make sure that there’s actually the possibility of benefit before we do this,” he says.

Charting Weight Changes on Hormone Therapy

The study relied on medical records of 132 men who underwent radical prostatectomies with subsequent androgen deprivation therapy at four Veterans Affairs hospital. The patients were enrolled in the Shared Equal Access Regional Cancer Hospital (SEARCH) database.

The average age of the study participants was 66. Half were white, 42% were African-American, and 8% came from other races.

A majority of men on ADT, 70%, gained weight -- an average of about 9 pounds per person. But 26% of men lost an average of 5 pounds each after starting ADT, and 4% saw no weight change.

In a subset of 84 men who had recorded weights for all three years of the study, researchers saw a distinct bump in weight during the first year on ADT, with no changes in the year before therapy or in the second year.

The study is published in the March issue of the urology journal BJUI.

Advice for Men Starting ADT

“When we discuss this in clinic as a potential and likely side effect, I tell patients that it’s hard for most men to maintain or lose weight, and androgen deprivation therapy is going to make that harder than it already was,” Saylor says.

Beyond weight gain, previous studies have shown that ADT causes changes in body composition -- a loss of muscle and bone mass with an increase in fat mass.

“So not only is the total amount of body weight going up, but it’s in the wrong proportions,” Freedland says. “It is a big problem.”

Those changes are thought to increase insulin resistance, which may, in turn, increase the risks for heart disease and diabetes.

“Our key tools for fighting against that really are diet and exercise,” Saylor says.

Freeland agrees, noting that there are studies under way to try to see what the best diets or exercise plans may best help men on hormone therapy peel off unwanted pounds, but the jury is still out on which is most effective.

In the meantime, he says the best guidance is the mantra followed by people who need to lose weight under any circumstances: Move more, eat less.